1. Field of the Invention
The present invention relates to a frequency modulated continuous wave (FMCW) radar device configured to measure a range, a relative velocity, an angle, and the like of an object to be measured (hereinafter referred to as “target”).
2. Description of the Related Art
Hitherto, an FMCW radar device is utilized as an on-vehicle radar device. For example, measurement results of a range, a relative velocity, an angle, and the like of a target, which are measured by the FMCW radar device, are used in a collision mitigation brake (CMB) system for decreasing damage when an own vehicle collides with a forward obstacle, and in an adaptive cruise control (ACC) system for tracking a forward vehicle.
In the related-art FMCW radar device, there is known a method of calculating the range, the relative velocity, and the like of the target by providing an up-chirp period in which a frequency of a transmission signal increases as time elapses and a down-chirp period in which the frequency of the transmission signal decreases as time elapses, and by pairing the peaks detected during the up-chirp period and the down-chirp period.
However, particularly in an on-vehicle environment, there are a large number of reflection objects on a road, such as guardrails, vehicles, humans, and walls, and hence reflections are obtained as many as the number of the reflection objects during the up-chirp period and the down-chirp period. Therefore, erroneous peaks may be paired at the time of pairing. As a result, a target that does not actually exist may be erroneously detected, or a target that actually exists may not be detected.
In view of this, as a method of reducing pairing errors in the FMCW radar, there is given a method of performing pairing assuming that a combination of peaks, which appear in a frequency spectrum of a reception signal and have substantially the same intensity, is obtained from the same target (for example, see Japanese Patent Application Laid-open No. Hei 4-343084).
Further, there is also given a method of reducing pairing errors by performing processing of tracking a beat frequency, to thereby calculate a range and a range change rate of the target based on beat frequency time-series data (for example, see Japanese Patent Application Laid-open No. 2010-19824).
However, the related art has the following problems.
In the related art disclosed in Japanese Patent Application Laid-open No. Hei 4-343084, pairing is performed with use of the peak intensity, and hence an erroneous pair may be obtained when there are a plurality of reflections having near peak intensities.
Further, in the related art described in Japanese Patent Application Laid-open No. 2010-19824, the range and the range change rate of the target are calculated before pairing by the processing of tracking the beat frequency, and then the pairing is performed, to thereby improve the pairing accuracy. However, this method assumes a linear uniform motion. Therefore, when the own vehicle and the target accelerate or decelerate and an error is caused in the range or the relative velocity calculated by the processing of tracking the beat frequency, differences between the range and the relative velocity during the up-chirp period and the range and the relative velocity during the down-chirp period are increased. As a result, there arises a problem in that correct pairing cannot be performed.